The invention concerns a stent, in particular a coronary stent, for expansion from a first condition into an expanded second condition in which it holds a vessel in an expanded condition, comprising a tubular body whose peripheral surface is formed by a number of annular support portions comprising bar elements which are connected in the longitudinal direction of the stent by way of connecting bars. The bar elements of at least a first support portion and a second support portion in adjacent relationship in a first direction extend in that case in a meander configuration in the peripheral direction of the stent and the connecting bars to the second support portion engage in the region of the turning points of the first support portion, which turning points face in the first direction.
A stent is what is known as an intraluminal expansion element which is used to hold a vessel, for example a blood vessel, in the human or animal body, in an expanded state. For that purpose the stent in a compressed first condition is moved by means of a suitable catheter to the location in the vessel, which is to be held in the expanded state. When the implantation location is reached the stent is radially expanded into an enlarged second condition. In the case of what is known as balloon-expansible stents the stent is expanded by means of a balloon catheter to such a great degree that, by virtue of plastic deformation, it maintains its expanded second condition even after removal of the balloon, and thus supports the vessel. In the case of what are referred to as self-expanding stents, the stent is held in a compressed first condition against a return force, for example by a sheathing catheter. That constraint is released at the implantation location so that the stent of its own accord assumes an expanded second condition.
Thus for example there is the known NIR-stentTM from Medinol Ltd., Tel Aviv, Ill., in which reversal or turning points which are respectively aligned with each other in the longitudinal direction of the stent, of two bar elements extending in a meander configuration, are-connected by way of an arcuate connecting bar. Known stents of that kind on the one hand frequently involve the problem that their position in the vessel once they have been placed and expanded, can only be corrected with difficulty, as a result of the biasing effect between the vessel and the stent. On the other hand, the problem which often already arises when moving the stent to the implantation location is that regions of the bar elements or the connecting bars, which project in the distal direction, that is to say in the direction of insertion, hookingly engage the wall of the vessel precisely in curved regions thereof, and are bent radially outwardly, which is frequently also referred to as xe2x80x9cfishscalingxe2x80x9d.
Therefore the object of the present invention is to provide a stent of the kind set forth in the opening part of this specification, which does not suffer from the above-indicated disadvantages or which suffers therefrom only to a lesser degree, and which in particular permits an easier variation in its position with respect to the vessel after expansion thereof.
Based on a stent as set forth in the classifying portion of claim 1, that object is attained by the features recited in the characterizing portion of claim 1.
The present invention is based on the technical teaching that a more easily repositional stent is obtained if at least two respective adjacent connecting bars engage in the region of a reversal or turning point of the second support portion, which turning point projects in a second direction in opposite relationship to the first direction. By virtue of the connecting bars being brought together in the region of a turning point of the bar element of the second support portion, when a tensile force is applied to the stent in the first direction, force components which are directed towards each other are exerted in the peripheral direction on the engagement points in question of the connecting bars on the bar element of the first support portion. They are thereby moved towards each other, whereby the diameter of the stent is reduced and thus the stent can be more easily displaced with respect to the vessel in the first direction.
In that arrangement the connecting bars do not necessarily have to be brought together at the turning point. They may also engage at a certain spacing from the turning point of the bar element of the second support portion.
In the same advantageous manner it is possible to use the stent according to the invention in conjunction with a sheathing catheter of correspondingly small outside diameter, into which the stent can be drawn by applying a suitable pulling force in the first direction for repositioning purposes, that is to say for correcting its position in the vessel, or which can be pushed over the stent for repositioning purposes.
Two and more adjacent connecting bars can engage the region of the turning point which projects in the second direction. Preferably however precisely two adjacent connecting bars engage the region of the turning point which projects in the second direction, as in that case then there is no further connecting bar to impede the movement towards each other of the two engagement points on the first support portion, thereby to produce a particularly effective reduction in diameter.
The bar elements of the first and second support portions can be arranged in any desired manner with respect to the peripheral direction of the stent. Preferably the bar elements of the first and second support portions extend substantially in phase with each other with respect to the peripheral direction of the stent, whereby a symmetrical configuration of the connecting bars with respect to the longitudinal direction of the stent and thus an advantageous uniform application of force to the bar elements is possible.
The connecting bars can be brought together at various turning points of the second support portion. Thus for example in the case of bar elements which are in phase with each other in the peripheral direction, it is possible for the connecting bars to be brought together respectively in the region of turning points, which are aligned with each other in the longitudinal direction of the stent, of the bar elements.
In preferred variants of the stent according to the invention the first support portion has first and second turning points which are in adjacent relationship in the peripheral direction of the stent and which project in the first direction and the region of which is engaged by connecting bars to different turning points of the second support portion. Arranged between those turning points is a third turning point which projects in the second direction and the region of which is engaged by the two connecting bars of a support portion in adjacent relationship in the second direction with the first support portion, with bar elements extending in a meander configuration in the peripheral direction of the stent. That arrangement affords particularly good distribution of the support locations for the vessel.
In further preferred embodiments of the stent according to the invention the bar elements and additionally or alternatively the connecting bars are adapted to increase the flexibility of the stent. That can be effected in many known ways.
Preferably for that purpose at least one support portion is formed by a bar element whose direction of curvature changes in the central region between two turning points. Additionally or alternatively at least the connecting bars between the first and second support portions are of a curved configuration, wherein their direction of curvature changes in the central region between the two points of engagement on the support portions. The respective S-shaped configuration reduces the stiffness of the elements in question, in the longitudinal direction of the stent, and thus enhances flexibility of the stent, with respect to its longitudinal axis. The stent can thus more easily follow curved vessel configurations.
Advantageous variants of the stent according to the invention are distinguished in that the bar elements and additionally or alternatively the connecting bars are adapted to achieve a stress distribution which is as uniform as possible upon deformation, in particular upon expansion of the stent. This also can be effected in many known ways.
Preferably for that purpose at least one support portion is formed by a bar element whose width decreases towards the center between two turning points. Additionally or alternatively the width of at least the connecting bars between the first and second support portions decreases towards the center between the two engagement points on the support portions.
In embodiments which are advantageous because they are simple to manufacture because of the simple geometry involved, at least one support portion is formed by a bar element which extends in a meander configuration in the peripheral direction of the stent, wherein each two bar element portions which are in adjacent relationship in the peripheral direction of the stent and which extend between the turning points form the limbs of a V-shape.
Further preferred variants of the stent according to the invention are distinguished in that the geometry of the bar portions and additionally or alternatively of the connecting bars is so selected that the stresses which occur therein upon expansion of the stent are above the elastic deformation limit and below the rupture limit of the stent material. Additionally or alternatively the width of the bar elements and additionally or alternatively of the connecting bars may vary over the length thereof in such a way that the stresses which occur therein upon expansion of the stent are above the elastic deformation limit and below the rupture limit of the stent material. That ensures that upon expansion the stent is advantageously substantially uniformly plastically deformed.